1. Field of the Invention
This invention relates to an optical disc recording method apparatus of a mark length recording system in which the laser light is illuminated on a recording surface of an optical disc to form pits for information recording. More particularly, it relates to a method and apparatus for recording an optical disc in which recording is made at a speed higher than a quadrupled speed, such as octupled or duodeca-tupled speed.
2. Description of Related Art
Up to now, in recording the information on a recording medium, such as an optical disc, in accordance with an optical modulation system, thermal control is exercised by pulsed light emission of the laser in order to form pits (marks) optimally on a disc. Specifically, the pulse waveform is set as a driving pulse for driving the laser, while the level (wave crest value) during each pulse period is also controlled to control the laser power and the laser illuminating period.
For example, in an optical recording and/or reproducing apparatus, typified by a CD-R (CD-Recordable) or CD-RW (CD-Re Writable), a pulse length controlling system or a pulse train recording system is used, in which the pulse length or the number of pulses of the laser light illuminated is varied depending on the recording mark length or space length to be recorded to control the laser power outputting domain.
The Orange-Book Part 2 (version 3.1), as the latest standard of CD-R, is premised, as the standard per se, on the mono-tupled speed, double-speed and quadrupled speed recording. The laser light emission control related to the write speed, that is recording strategy (recording compensation) is prescribed as shown in FIGS. 1 and 2. That is, in the CD-R standard, the information is recorded on an optical disc by the combination of pits (marks) and lands (spaces) of 3T to 11T. For the recording strategy for mono-tupled speed and double-speed recording, the laser power outputting domain of(nxe2x88x92xcex8)T+xcex1T is prescribed, where xcex8=1T and xcex1=0.13T, with the laser power forming nT pits (marks) being Pw, as shown in FIG. 1. For the recording strategy for quadrupled speed recording, (nxe2x88x92xcex8)T and ODT are prescribed as being output domains of the laser power Pw and the laser power xcex94P, respectively, with the laser power forming nT pits (marks) being Pw+xcex94P, where xcex94P is 20 to 30% of Pw and ODT is set to 1.25T to 1.5T. It is noted that the mono-tupled speed herein means a speed of 1.2 to 1.4 m/s with the disc being run in rotation at a constant linear velocity (CLV).
Meanwhile, if the recording strategy prescribed by the above-mentioned Orange Book standard, premised on the mono-tupled speed recording, double speed recording and on the quadrupled speed recording, is to be applied to recording at a speed higher than the quadrupled speed, such as octupled speed recording or duodeca-tupled speed recording, thermal interference occurs between the pit and land codes to be recorded, with the result that recording signals are deteriorated in signal quality due to deformed pit shape or to increased jitter.
That is, the ideal relation between recording data and pits is such that, for recording data with a length equal to nT, a pit with a length equal to nT is formed to an oblong shape, as shown in FIG. 3. If now the octupled speed recording, for example, is to be made with the recording strategy for mono-tupled speed recording and double speed recording, a tear-shaped pit is formed in which the trailing end side of the pit is spread in a direction perpendicular to the track center, as shown in FIG. 4. If the recording strategy for quadrupled speed recording is used, there is again formed a tear-shaped pit which is only slightly improved over the case of the octupled speed recording as to spreading of the pit in the direction perpendicular to the track center, as shown in FIG. 5.
In FIGS. 4 and 5, the time periods A and B denote time delay as from the turning on of the laser emission until start of the pit forming process. On the other hand, the time periods a, b and c denote time delay as from the turning off of the laser light emission until termination of the pit forming process.
If the recording signal is deteriorated in quality due to deformed pit shape or increased jitter, there is a risk that regular reproduction cannot be realized.
It is therefore an object of the present invention to provide an optical disc recording method and apparatus whereby pits can be formed to an optimal shape at a speed faster than the quadrupled speed, such as an octupled speed or duodeca-tupled speed.
In one aspect, the present invention provides an optical disc recording apparatus including recording pulse generating means for setting a recording power at approximately the leading end portion of a recording pulse in steps of a plurality of stages and for generating a recording pulse of a pulse width corresponding to a length of a pit to be formed, and laser means for illuminating the laser light by the recording pulse supplied to form a recording data string comprised of pits and lands defined between the lands on a recording medium, wherein the laser light emitting pulsed light by the recording pulse generated by the recording pulse generating means is illuminated on a write-once optical disc as the recording medium to effect recording.
In another aspect, the present invention provides a recording method for an optical disc including generating a recording pulse having a pulse width corresponding to a length of a pit formed, the recording pulse being so formed that a recording power at approximately the forward end thereof is stepped over plural stages and illuminating a laser light beam, excited in pulsed light by the recording pulse, on a write-once optical disc to effect recording.
In still another aspect, the present invention provides a recording apparatus for an optical recording medium including means for causing rotation of the recording medium, a controller for controlling the rotational speed of the rotating means, laser means for illuminating the laser light by drive pulses supplied to form a recording data string including a pit and lands ahead and at back of the pit on the recording medium, drive pulse generating means for generating a first pulse corresponding to recording data, a second pulse for synthesis to a leading end of the first pulse and a third pulse for synthesis to a leading end of the first pulse, and for synthesizing the first to third pulses to generate the drive pulse, and pulse generation controlling means for performing control so that the level or the pulse width of one or more of the first to third pulses generated by the drive pulse generating means is varied depending on at least one of the lengths of the pit and the land formed.
In yet another aspect, the present invention provides a recording method for forming a recording data string including generating a first pulse corresponding to recording data, a second pulse for synthesis to a leading end of the first pulse and a third pulse for synthesis to a leading end of the first pulse, as pulses the level or the pulse duration of which is varied depending on at least one of the length of the pit formed and the length of the land formed, synthesizing the first to third pulses to generate a recording pulse, and illuminating the laser light by the drive pulse to form a recording data string including pits and lands between for and aft side pits on a recording medium rotated at a pre-set speed.
According to the present invention, as described above, in which the recording pulse with a pulse width corresponding to a length of a pit formed, having a recording power at approximately the forward end thereof stepped over plural stages, is generated, and the laser light excited into pulsed light by the recording pulse is illuminated to effect recording, it becomes possible to reduce thermal interference due to inter-symbol interference between the codes, that is the pits and the lands recorded, with the result that pits/lands may be formed to an optimum shape to enable a sufficient replay margin to be produced even at a high-speed recording such as octupled speed recording. In addition, the recording quality may be improved through reduction in the recording jitter.
That is, with the present invention, recording with optimal pit shape may be achieved at a speed higher than the quadrupled speed, such as at an octupled or duodeca-tupled speed.